What do you think is happening?

[Neverdone]

So having car troubles again....... poor old black betty, my truck a 96 Z71 with a 305. I suspect she is getting ready for the final round up.

She has 174,000 miles, 74,000 miles I put on myself over the course of the last 8 years. By the way that is all on the original motor, trans, axles, bearings, drive shafts, u-joints, everything. And she hasn't lived an easy life for a half ton. She has spent a lot of time dragging a trailer with my jeep on it and other things..... Put on a dual straight pipe exhaust many moons ago, K&N cold air intake, throttle body spacer, and an aux 10,000# trans cooler. Other than that she is stock.

Couple days ago I took off from a buddies house and she sounded pretty rattly.... ...... Only a couple times taking off from a stop sign.

Drove it to work last couple days. When it is cold as in not ran for a few hours and you start it up it sounds fine idling. But when you take off it sounds rattly again . Also it has high oil pressure. Normal for the truck when the motor is cool is 60psi running warmed up 40psi running. Idle it sits around 40 psi cool and 20psi warm. This morning it had about 70psi when I pulled out of the driveway under acceleration then backed off to 60 psi. 5 miles down the road I stopped at a stop sign and everything was normal.

My personal experience tells me it is not a rod knock just because of the fact that it doesn't do it all the time, but the fact that the oil pressure is a little high makes me think there is a bearing walking around [S.

My only other thought is that it is a piston slap but I am not sure.

I do know that the catalytic converter is on its way out. That has been dancing around for quite some time (really annoying sounding). Thinking I am going to cut the cat off and put up a test pipe just to be sure that is not it. But after that, don't know. She has fresh oil 800 miles ago, pulled the stick yesterday and it is full and actually looked pretty clean for having that much time on it.

Anybody else have any thoughts?

I would hate to see old betty go, but sometimes you just have to let them....

 

[Old Iron]

Can't explain the oil pressure but, ya might check the knock sensor may need a new one.

 

[maverickmk]

I would take a look at the catalytic converter. My wife used to have a Cadillac SRX (that car was a piece of crap) that the inner ceramic unit had come unglued/unattached from the metal casing. It rattled under light acceleration and idling. Sometimes it would get stuck and stop rattling, then it would loosen up and start rattling again. That might be it, but as for the oil pressure, could be a bad sensor, bad gauge or, like you said, a bearing getting ready to let loose.

 

[Dr Crankenstein]

Just a couple of thoughts to add...

Oil pressure.
- I would expect it to be lower than normal if you're losing a rod bearing, especially at operating temperature. [S
- It's possible you have a blocked filter and it's bypassing.
- You're running a "fatter" oil, like 10W-30 instead of 5W-30.

Knock.

- Could be the timing chain rattlin'.
- As much as I hate to say it, maybe crankshaft thrust bearing.

 

[Old Iron]

May also be a cracked tranny flex plate
They crack right around where it bolts to the crank.

 

[Neverdone]

Just a couple of thoughts to add...

Oil pressure.
- I would expect it to be lower than normal if you're losing a rod bearing, especially at operating temperature. [S
- It's possible you have a blocked filter and it's bypassing.
- You're running a "fatter" oil, like 10W-30 instead of 5W-30.

Knock.

- Could be the timing chain rattlin'.
- As much as I hate to say it, maybe crankshaft thrust bearing.

Always run 10w-30. Never put anything else in. Is there anyway to check the thrust bearing? Its coming from the rear so doubt its the timing chain.

Old iron thanks i will check the flex plate.

I doubt its a bearing now. I just towed my rat 100 miles with it today and the noise doesnt seem as loud now. Laid under it last night and listened to it. I think its the cat. Figured if it was a bearing it would have come unglued today towing.

 

[Dr Crankenstein]

Damn cats! I hope it's the converter and that's the end of it.

Is there anyway to check the thrust bearing? Its coming from the rear so doubt its the timing chain.

Throw a timing light on it. Make a mark across the timing mark. If the thrust bearing is really whacked, you should see the crank "walk" back and forth when it's running. Same goes for the chain. If it's sloppy the timing mark will float around.

 

[offroadrolls]

Damn cats! I hope it's the converter and that's the end of it.




Throw a timing light on it. Make a mark across the timing mark. If the thrust bearing is really whacked, you should see the crank "walk" back and forth when it's running. Same goes for the chain. If it's sloppy the timing mark will float around.

Also, if you can get a hold of the crank pulley from below you'd be able to push pull it back an forth if it had excessive end play. Maybe use something soft to pry on it. I have an 81 GMC with a 350 that some dummy used washers to shim between the converter and the flex plate. Problem was the converter had no float and ended up wiping out the thrust bearings.

 

[Neverdone]

Thanks guys will give that a shot next week. Taking vaca at work for the week so I will look into it.

 

[Neverdone]

Welp..... I think it is the beginning of the end of the tired 305 in old Betty.

I put a can of motor flush in Wednesday morning and let her run for a couple minutes while I wiped out my oil drip pan (to insure the pan was clean when I started for inspection purposes). Drained the oil into a jug and looked at the bottom of the drip pan. Found what I expected/didn't want to see, metal. Not a bunch, but enough. The motor hasn't been sounding any worse, its not smoking, nothing to make me think it will fail soon, but I fear the end is near.

 

[Dirtyrat]

Why not pull the pan and inspect bearings? if they all look good, how about replacing the oil pump?

 

[Neverdone]

Probably could, but that motor has 175,xxx miles so might as well overhaul/upgrade, and in order to drop the pan on that motor you have to either pull it or drop the front end. I suppose the oil pump is a possibility though. I will look into that and see what happens...... until then I am on the look out for a long block 350 (upgrading).....